饮其流者怀其源，学其成时念吾师。
Drink the flow with a source, read my teacher when you learn it.
潮白河流域密怀山前地区处于古北口—天竺东北信风带 ，自然和人为因素导致风沙化环境渐趋强烈 ，成为首都沙尘暴天气中就地起沙的源区之一。
Natural and man made factors make sand blown by wind environment, one of sourse regions of sand getting up on the spot during capital sand dust devil weathers, worse and worse.
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